In a multi-track vehicle, if it travels around a curve, the wheels of one axle run over curved paths of different diameters. Since the turnable-outer wheels cover a longer path than the turnable-inner wheels, they have different speeds if no slippage occurs between the ground and the wheels. If the wheels are now driven together, precautions that permit suitably different speeds on the wheels without tensions resulting between the wheels themselves and in the drive train have to be taken. Differentials or clutches, which distribute or interrupt the drive to the wheels when cornering serve this purpose.
In EP-A 02 39 763 is described a driven axle for motor vehicles having two free-wheel clutches both of which transmit to the synchronously rotating wheezes the power of an engine when traveling straight ahead. During a travel condition with varying ground adherence of the wheels, such as with one wheel upon ice and the other wheel on gripping solid soil, the engine power, when the clutches are engaged, is transmitted to each wheel in proportion to the adhesion limiting value so that optimal traction values are obtained.
When cornering, a free-wheel clutch interrupts the drive to a wheel, especially to the turnable-outer wheel that runs more quickly during a traction operation. The free-wheel clutches, therefore, allow the separation of the wheels or rigid transmission function depending on the travel condition.
An expansion device contains a cylindrical bolt as a supporting element and annular pistons provided with cams. The annular pistons are rotatable relative to the supporting element. The supporting element firmly connected with the housing of the free-wheel clutches rotates during stress cycle in the drive relative to the annular pistons and pressurizes the annular pistons in an axial direction. If in the traction operation one of the wheels of the axle rotates more quickly than the opposite wheel, its annular piston rotates in advance relative to the supporting element in a drive direction so that the cams release themselves from the expansion device and the disengaged clutch interrupts the connection between drive and quicker wheel. Separately disposed cams are provided on the annular pistons for forward and reverse travel.
The rotation in the direction of travel of the annular piston of the clutch which leads to the quicker wheel has to be limited in a manner such that its cam surface remains free for the opposite direction of travel. Otherwise, the clutch could be engaged again by the cam surface for the opposite direction of travel and stresses result in the drive train.
In the above cited publication is described a clip which limits the torsion clearance of the annular pistons. When cornering, the clip holds the annular piston leading to the turnable-outer quicker wheel in a neutral position free of axial force as long as the supporting element with the opposite annular piston holds its clutch engaged and connects the turnable-inner wheel with the drive. For a stress-free operation, two driving modes are provided:
cornering with a leading wheel and a driven wheel of an axle, and PA1 straight-ahead travel. PA1 makes possible the free wheeling of both the turnable-inner and turnable-outer wheels lock in case of angles of larger than a specific steering angle of the steered wheels of an axle, PA1 separates the quicker turnable-outer wheel from the drive and connects the turnable-inner wheel with the drive in case of angles of lock smaller than a specific steering angle of the steered wheels, PA1 drives synchronously both wheels of an axle in case of straight-ahead travel.
Agricultural vehicles reach angles of lock of the steered wheel larger than 50 degrees. The turnable-inner and turnable-outer steered wheels of a front axle run from a specific steering angle larger than about 35 degrees, for instance, to curved paths larger than the curved path of the central rear axle. If the motor vehicle is all-wheel driven, the wheels of the steered front axle in the presence of an adequate transmission ratio between front and rear axles, are in a coasting operation away from the specific steering angle.
If one of the steered wheels is in a coasting operation, as result of its large path radius and remains, at the same time, rigidly connected with the drive, slippage occurs on this wheel and on the wheels still in a traction operation when there is an elevated load of the drive.
For stress-free operation of an all-wheel drive with a steering angle larger than a specific steering angle of about 35 degrees, for instance, both steered wheels of a driven front axle should therefore run freely in order to keep the drive free of additional stresses and to operate the motor vehicle with improved efficiency.